Method for the production of axially symmetrical workpieces with or without a toothed profile

ABSTRACT

The method according to the invention for producing substantially axially symmetrical workpieces by shaping a starting material uses a die and a rotatable tool, the die being provided with a bore along the central axis thereof. Here the starting material is introduced through the bore of the die and pressed in between the die and the rotating tool such that the starting material flows outward from the central axis according to the contour of the die. The workpiece is thus produced in a single operation. Depending on the requirements for the dimensional accuracy and surface quality, mechanical finishing or calibrations are possible. Due to the material flow in the die and the rotation of the tool, shaping forces which are only small in comparison to conventional methods occur here, and so the requirements made of the tools, and so the expense, are reduced. Since the shaping takes place without cutting, the resulting fibre flow of the finished workpiece is also advantageous and provides the workpiece with better mechanical properties.

PRIORITY CLAIM

This application claims the benefit of EP-05 015 102.6, filed on Jul. 12, 2005.

TECHNICAL FIELD

The present invention relates to a method for the production, without cutting, of substantially axially symmetrical workpieces, in particular workpieces with a toothed profile, and a workpiece produced with the method.

BACKGROUND ART

Previous methods known from the prior art which produce axially symmetrical workpieces, such as e.g. crown gears by shaping, without cutting, are characterised above all by the cost-intensive tools which are required. During the shaping processes strong shaping forces occur which bring about stresses with partly extreme fatigue stress peaks in the tools, and this has a negative effect upon the life of the tools, and so upon the cost of the latter.

One can give axial roll forging as an example of this type of conventional method. Here the whole volume of material to be shaped must be placed from the start between the shaping tools and must be correspondingly pre-shaped, and this additionally increases the labour input. With axial roll forging too the approach angle of the tool must be held within a precisely controlled range, and further parameters such as the rolling speed must be observed, and this of course makes production even more complicated.

DISCLOSURE OF INVENTION

Therefore, it is the object of the present invention to develop a method for producing substantially axially symmetrical workpieces, in particular with toothed profiles, which enables more simple, and therefore faster and less expensive processing.

This object is fulfilled by a method with the features of claim 1. Advantageous embodiments follow from the sub-claims.

The method according to the invention for producing substantially axially symmetrical workpieces by shaping a starting material uses a die and a rotatable tool, the die being provided with a bore along the central axis thereof. Here the starting material is introduced through the bore of the die and pressed in between the die and the rotating tool such that the starting material flows outward from the central axis according to the contour of the die. The workpiece is thus produced in a single operation. Depending on the requirements for the dimensional accuracy and surface quality, mechanical finishing or calibrations are possible. Due to the material flow in the die and the rotation of the tool, shaping forces which are only small in comparison to conventional methods occur here, and so the requirements made of the tools, and so the expense, are reduced. Since the shaping takes place without cutting, the resulting fibre flow of the finished workpiece is also advantageous and provides the workpiece with better mechanical properties.

Advantageously, the method is further characterised in that the starting material can be introduced continuously and in a controlled manner into the space between the die and the tool. In this way the quantity of material to be shaped per unit of time can be adapted optimally to the chosen shaping conditions, and this additionally keeps the required shaping forces within limits.

According to one advantageous embodiment the die is mounted in a fixed position. Therefore, the shaping is only determined by the feed rate of the material and the rotational speed of the tool, and so simple, cost-efficient control of the method can be used.

However, the die can also preferably be mounted rotatably about a rotation axis, and this opens up new possibilities for controlling the shaping without however substantially complicating the control.

In order to obtain further control possibilities, the rotation speed of the die is preferably controlled independently of the rotation speed of the tool; however, the die can also run freely with the rotating tool. Any friction occurring between the material and the tool can thus be controlled, and this leads to an exceptionally even flow of material with consequently improved properties of the end product.

In one preferred embodiment the rotation speed n of the tool and/or the distance a between the tool and the die is set during shaping. The shaping can thus be adapted to the given circumstances even when the method is already underway.

For applications in which it is desirable to keep the friction surface located between the workpiece to be shaped in the die and the tool high, the central axis of the die and the rotation axis of the tool can be in alignment. If however lower friction, i.e. a smaller friction surface, is desired, as for example with solid workpieces, according to a further preferred embodiment the rotation axis of the tool can be offset in relation to the central axis of the die with an excentricity e. The level of excentricity can preferably by set by the rotating tool being rotated, oscillating, about the central axis of the region of the workpiece to be shaped. The excentricity is adapted here to the starting material to be shaped and to the outer dimensions of the workpiece to be produced. The oscillation is achieved, for example, by a radial feed movement of the tool. Moreover, the reduction in the friction surface has the advantage of less force and so energy being required for the shaping due to the contact which is only partial.

In order to achieve optimal mould filling of the die, in one preferred embodiment the die has an edge which is preferably profiled. The method according to the invention is therefore particularly advantageous for the production, without cutting, of workpieces with toothed profiles. Due to the even flow of material and the filling of the mould in the die during shaping, precise profiling of the workpiece on the front side, e.g. front toothing, is made possible.

Preferably, the starting material is heated up during the step of introducing or pressing in. In this way the flow properties of the material are improved, by means of which shaping forces are further reduced.

With the method according to the invention, not only solid but also hollow starting materials can be shaped. This means that the starting material is preferably introduced in solid or tubular form through the bore of the die and into the space between the die and the tool. Therefore, with tubular material it is also possible to change the flow direction in the die.

Advantageously, the tool has a symmetrical or asymmetrical tool contour. Whereas the one side of the finished workpiece is determined by the shape or contour of the die, using a tool with a symmetrical or asymmetrical contour makes it possible to influence the shape of the other side in many ways.

A workpiece produced with the method, without cutting, according to the invention is accordingly characterised by a continuous and non-interrupted fibre flow substantially parallel to the integrally moulded surface contour. This type of fibre flow increases the loading capacity of the material, its life and freedom from defects, and so the overall quality of the workpiece. Moreover, the finished workpiece is produced in a substantially shorter time, and this has a positive effect upon the cost:benefit ratio.

BRIEF DESCRIPTION OF DRAWINGS

In the following the invention is described by means of an exemplary embodiment according to FIG. 1.

FIG. 1 shows a diagrammatic perspective view of a die used in the method according to the invention and of a tool, the material flow being indicated.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 diagrammatically illustrates a tool design which shows a die 1 and a tool 2 disposed over the latter. The die has a bore 11 through its central axis and a contour in the form of toothed profiling 12 and an edge 13 on the side facing towards the tool. The tool is rotated with a rotation speed n, and the distance a between the tool and the die can be set by a feed movement. The starting material 3 is continuously introduced by a ram (not shown) with a feed speed into the bore 11 (arrow S), from where it is pressed into the space between the contour 12 of the die and the tool 2. By pressing in and rotating the tool acting upon the material, the material flows radially outwards along the contour of the die until it finally fills the mould of the die with material due to the edge 13, and produces the finished workpiece. Here the distance a is also adapted to the quantity of material in the die. The material feed is controlled such that only as much material is pressed in as is required for shaping under the given conditions.

The method disclosed in the following patent claims makes it possible to produce axially symmetrical workpieces from solid or tubular starting material by shaping without cutting, with or without a toothed profile. The person skilled in the art will doubtlessly identify further advantageous embodiments by means of the example illustrated here which also come within the scope of this invention. 

1. A method for producing substantially axially symmetrical workpieces by shaping a starting material (3) with the aid of a die (1) and a rotatable tool (2), the die being provided with a bore (11) along the central axis thereof, and which comprises the following steps: introducing the starting material through the bore of the die; pressing the starting material in between the die and the rotating tool such that the starting material flows outward from the central axis according to the contour (12) of the die.
 2. The method according to claim 1, the starting material being introduced continuously and in a controlled manner.
 3. The method according to claim 1 or 2, the die being mounted in a fixed position.
 4. The method according to claim 1 or 2, the die being mounted rotatably about a rotation axis.
 5. The method according to claim 4, the rotation speed of the die being controlled independently of the rotation speed of the tool.
 6. The method according to claim 4, the die running freely with the rotating tool.
 7. The method according to any of the preceding claims, the rotation speed n of the tool and/or the distance a between the tool and the die being set during shaping.
 8. The method according to any of the preceding claims, it being possible to offset the rotation axis of the tool in relation to the central axis of the die with an excentricity e.
 9. The method according to claim 8, the level of excentricity being set by the rotating tool being rotated, oscillating, about the central axis of the die.
 10. The method according to any of the preceding claims, the die having a preferably profiled edge (13).
 11. The method according to any of the preceding claims, the starting material being heating up during the step of introducing or pressing in.
 12. The method according to any of the preceding claims, the starting material being introduced in solid or tubular form.
 13. The method according to any of the preceding claims, the tool having a symmetrical or asymmetrical tool contour.
 14. A workpiece produced with the method according to any of claims 1 to 13, characterised in that it has continuous and non-interrupted fibres substantially parallel to the integrally moulded surface contours. 